Artificial lift for oil wells

ABSTRACT

An apparatus for retrieving oil from a producing zone after the bottom hole pressure has decreased to such an extent that artificial lift is required for production. An accumulator is positioned in the area of the casing where oil accumulates with the uppermost portion being vented to atmosphere to allow oil flow therein. A floating piston-type device may be located immediately above the accumulator with a bypass from the accumulator to the top of the following piston. Pressure is subsequently applied through the vent line to the accumulator to force oil from the accumulator through a stinger tube above the floating piston and subsequently raise the oil and floating piston to the surface. Without the piston, a stinger tube and standing valve may be used to accumulate oil in the production tubing.

United States Patent [1 1 Morgan ARTIFICIAL LIFT FOR OIL WELLS Thomas11. Morgan, 800 NW. Loop 410, San Antonio, Tex. 78216 [22] Filed: June4, 1974 [21] Appl. No.: 476,212

[76] Inventor:

POWER SOURCE ATMOSP ERE July 15, 1975 Primary Examiner-C. J. HusarAssistant ExaminerRichard E. Gluck Attorney, Agent, or FirmCox, Smith,Smith, Hale & Guenther [57] ABSTRACT An apparatus for retrieving oilfrom a producing zone after the bottom hole pressure has decreased tosuch an extent that artificial lift is required for production. Anaccumulator is positioned in the area of the casing where oilaccumulates with the uppermost portion being vented to atmosphere toallow oil flow therein. A floating piston-type device may be locatedimmediately above the accumulator with a bypass from the accumulator tothe top of the following piston. Pressure is subsequently appliedthrough the vent line to the accumulator to force oil from theaccumulator through a stinger tube above the floating piston andsubsequently raise the oil and floating piston to the surface. Withoutthe piston, a stinger tube and stand ing valve may be used to accumulateoil in the production tubing.

4 Claims, 3 Drawing Figures ARTIFICIAL LIFT FOR on. WELLS BACKGROUND OFTHE INVENTION This invention relates to oil recovery devices and, morespecifically, to an artificial lift for recovering oil from wells thatdo not have sufficient bottom hole pressure to raise the oil to thesurface. The apparatus includes an accumulator to receive the oil in thecasing and a vent line to the surface which may subsequently bepressurized to raise the oil contained in the accumulator into theproduction tubing and subsequently the well head.

DESCRIPTION OF THE PRIOR ART There are several stages in the productivelife of an oil well that should be reviewed before going tinto thedetails of the present invention. When a hydrocarbon producing well (oilwell) is drilled, the initial stage of production normally does notrequire any type of lift mechanism to raise the oil from the producingformation to the well head. The pressure on the oil itself is sufficientto raise the petroleum (gas and oil) to the well head. As oil isproduced from the oil reservoir, the bottom hole pressure will continueto drop until it reaches a point where the bottom hole pressure is nolonger sufficient to raise the column of oil to the well head.

once the bottom hole pressure has reduced to such an extent that it willno longer raise the column of oil to the well head, steps can be takento reduce the weight of the column. A column of fluid from the oilreservoir to the well head that does not contain gas weighs more than acolumn that does contain gas. Therefore, a system called gas lift andcommonly used by the petroleum industry is to bubble gas up through thecolumn of oil thereby reducing the weight of the column and to cause theoil from the well to continue to flow. Now the bottom hole pressure issufficient to raise the lightened column to the well head for a normalproduction flow. This continues until the bottom hole pressure is againreduced to a greater degree so that it is no longer sufficient to raisethe lightened column to the surface of the well.

The next stage in the productive life of an oil well under present dayoperating conditions would be to allow the oil to accumulate in thetubing and then to pressurize the casing. By having a gas lift valvebelow the oil accumulated in the tubing, a blob of oil could be raisedto the surface. Thereafter, the pressure on the casing would be relievedand oil would be allowed to accumulate again in the tubing. This processis repeated again and again by allowing oil to accumulate in the tubing,pressurizing the casing and raising the blob of oil to the well head andrelieving the pressure to allow oil accumulated again in the tubing.This process has been aided somewhat by the use of swabs or subsurfaceplungers (commonly called free floating pistons) with the swabs orplungers allowing the oil to accumulate above their location in theproduction tubing. Thereafter, further pressure increases in the casingwould raise both the oil and the swab or plunger to the surface.Subsequently, the swab or plunger would be allowed to fall back to itsoriginal position in the tubing and the cycle repeated.

Because the casing, which is alternately pressurized and depressurized,can only stand a certain amount of pressure, even the type of gas liftjust described has limited application. At this stage of the productivelife of the well, some type of subsurface pump is needed to raise oil tothe surface of the well. Bottom hole pumps are very expensive, wear outand must be replaced periodically. It becomes a matter of economics asto when the bottom hole pressure is no longer sufficient to dischargeenough oil from the well to justify the cost of maintaining the costlywell equipment. At this point in time, the well is usually abandonedunless other drastic steps such as flooding the production zone areused. At this particular point the bottom hole pressure has dropped tosubstantially zero.

Some production has occurred in old petroleum fields by drilling holeswell below the productive zone. Actions such as latent water drives,formation compression, gravity and many other contributing factors maycause oil to gradually fill the holes drilled below the productive zone.However, to remove the oil that has accumulated in the hole drilledbelow the productive zone (commonly called sump bores) is very costly,again requiring some type of subsurface pump to raise the oil to thesurface of the well. Such production is normally economicallyunfeasible.

It should be noted in the previously described gas lift systems that agas source may be necessary; however, most of the gas used in liftingcan be recovered through a tank separator. Air could not be used becauseof the mixing of the air and oil to cause an emulsion.

SUMMARY OF THE INVENTION The present invention is directed towards aneconomical means and apparatus for continuing production of an oil wellafter it becomes economically unfeasible using normal productiontechniques. An accumulator is positioned in the oil that naturallydrains into the oil well. A vent line allows the accumulator to be atthe same pressure as atmosphere so that the oil will fill theaccumulator. Thereafter, the accumulator is pressurized through the ventline, forcing the oil through a standing valve and stringer tube intothe production tubing. In the embodiment using a floating piston orswab, a bypass line moves the oil above the free floating piston orswab. As the pressure further increases in the accumulator, a gas liftvalve below the free floating piston or swab will open, thereby causingthe piston and oil accumulated above the piston to rise to the surfaceof the well. Once the piston has reached the top of the well, pressurein the accumulator is vented through the oil line to further kick theoil into the oil tank and, simultaneously, the piston is allowed to fallback into its position immediately above the accumulator. As oil againcollects in the accumulator the previously mentioned cycle is repeated.A ball float valve in the air line tells an electronic control circuitand an associated pressure switch when the accumulator has been filled;therefore, it is time to pressurize the accumulator and raise the oil tothe surface. An appropriate clock mechanism is used to time the cyle tocontrol the compressed air in and out of the accumulator.

In another embodiment, the stinger tube simply feeds through a seal areaabove the accumulator into the production tubing. Upon pressurizing theaccumulator, oil moves through the standing valve and stinger tube intothe production tubing. Pressure is then relieved and oil again collectsin the accumulator with the standing valve preventing the previouscollected oil from feeding back from the production tubing into theaccumulator. By alternately venting and pressurizing the accumulator,the oil is moved up the production tubing to the well head. Once the oilhas been collected in the accumulator, it is never lost, and once theoil enters the production tubing, it never reenters the accumulator.

Therefore, it is an object of the present invention to provide anapparatus for gathering oil from a well once the well has stoppedflowing due to a decrease in pressure of the reservoir.

It is a further object of the present invention to provide artificiallift for an oil well that utilizes the minimum of equipment so that itis economically feasible to continue production from an oil well inranges of approximately one barrel per day.

It is still another object of the present invention to position anaccumulator in oil that would naturally accumulate in the bottom of thewell, vent the top of the accumulator to the atmosphere to allow oil toflow through a check valve into the accumulator, subsequentlypressurizing the accumulator, thereby forcing oil up through a stringertube and bypass tube to a position above a free floating piston or swab,and by continued pressurization operating a gas lift valve to lift thefree floating piston or swab with the oil contained thereabove to thewell head.

It is yet another object of the present invention to use a ball floatvalve in the vent line in combination with a pressure switch and chokelocated at the surface to give a signal indication when the accumulatoris full of oil. The signal is then used to trigger control circuitrythat would be used to pressurize the accumulator.

It is still another object of the present invention to use a gas liftvalve underneath the free floating piston or swab so that pressure inthe accumulator must exceed a certain point before the free floatingpiston or swab will begin to rise to the surface. The gas lift valveshould be set for a sufficiently high pressure so that almost all of theoil in the accumulator is raised above the free floating piston or swabbefore the gas lift valve opens.

It is yet another object of the present invention to provide aretrievable apparatus immediately above the accumulator to allow directaccess to the accumulator and to the bottom of the well.

It is yet another object of the present invention to provide a systemthat can be used in the producing of an oil field wherein each of thewells in the oil field have a low volume output and require some type ofartificial lift.

Yet another object of the present invention is to provide an accumulatorlocated in the oil that collects in the casing, the accumulator beingalternately vented to the atmosphere to collect oil and pressurized toforce the oil through a standing valve in a stinger tube into theproduction tubing, the oil column in the production tubing continuallyincreasing until it reaches the well head and flows with each cycle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevated sectional viewof the artificial lift apparatus of the present invention and theassociated controls.

FIG. 2 is an elevated partial view of FIG. 1 showing an alternativeembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawings in conjunction with the following specification, a betterunderstanding of the invention can be obtained. A hydrocarbon producingwell represented generally by the reference numeral I0 is shown in asectional view with the casing of the well being represented byreference numeral 12. The casing 12 of the well 10 extends down throughthe earth 14 to a hydrocarbon producing zone 16 located some distancebelow the earths crust. The casing I2 is usually cemented into place bycement 18 near the surface of the well. In the hydrocarbon producingzone 16 the casing 12 has perforations 20 to allow a substance such asoil from the hydrocarbon producing zone 16 to flow into the casing 12.At the top of the casing 12 there is located a casing head clamp 22 thatmay or may not seal off the well head according to the circumstances ofthe individual well. In conjunction with the present invention, thecasing head clamp 22 is shown with a vented well head through opening24.

From the well head production tubing 26 and vent- /compressor line 28 isrun into the well. It should be noted that the vent/compressor line 28is a fairly small diameter line with an inside diameter of probably lessthan one inch; however, the production tubing 26 could be several inchesin diameter. The bottom of the production tubing 26 has an expandeddiameter to form an accumulator 30 which may be located in thehydrocarbon producing zone 16. However, accumulator 30 need only beinserted in the well 10 to such a depth that oil from the hydrocarbonproducing zone 16 will accumulate therein. This depth may be above orbelow the hydrocarbon producing zone 16. At the bottom of theaccumulator 30 is a check valve 32 that allows oil to enter throughopening 34 into accumulator 30. Check valve 32 prevents the oil fromdraining from accumulator 30 once it has been collected therein. Thecheck valve 32 may be constructed as a standing valve so that is may beretrieved from the surface and access be obtained to the bottom of thewell 10 without removing the accumulator 30.

The vent/compressor line 28 extends down inside of accumulator 30through opening 36 in an airtight manner. Opening 36 is attached to thevent/compressor line 28 by any conventional means such as welding.Immediately inside of accumulator 30 the vent/compressor line 28 isattached to a ball float chamber 38. The ball float chamber 38 has aball valve 40 inside of housing 42 which has perforations 44 in the sideand bottom thereof. The ball float chamber 38 is designed so that theball 40 will begin to float as fluid in accumulator 30 collects to suchan extent that it begins to enter ball float chamber 38 through theperforations 44. As ball valve 40 reaches the top of housing 42 it willseat against the opening between vent/compressor line 28 and housing 42,thereby terminating the venting of ac cumulator 30 through thevent/compressor line 28.

Immediately above the accumulator 30 in the production tubing 26 islocated a seal disc 46, space 48 and another seal disc 50. The sealdiscs 46 and 50 are made in one integral unit though not shown as suchin FIG. 1 for illustration purposes. Seal disc 50 rests against shoulder47 of casing 26. The circumference of the seal discs 46 and 50 isexpandable to form retrievable seal 49. Retrievable seal 49 may beexpanded after positioning to very rigidly seal the seal discs 46 and 50to casing 26 in a manner common to the petroleum industry. Hook 124attached to the upper surface of seal disc 46 provides a means by whichseal discs 46 and S0 and components connected thereto may be retrievedfrom the well 10.

Extending through seal discs 46 and 50 is a pressure line 52 which has agas lift valve 54 connected to the lower end thereof. The gas lift valve54 is of the traditional type having a ball 56 pushed against seat 58 bya bellows 60 which receives external pressure through opening 62. Thegas lift valve 54 is designed with the bellows 60 having a largerpressure area inside of valve 54 than ball 56 so that once a certainpressure external to the gas lift valve is reached the ball 56 willunseat thereby allowing the pressure to flow through pressure line 52and past seal discs 46 and 50.

A stinger tube 64 extends from space 48 through seal disc 50 to a pointnear the bottom of accumulator 30. At the bottom of stinger tube 64 is astanding valve 122 to allow oil collected in accumulator 30 to flow intothe stinger tube 64. The standing valve 122 operates in much the samemanner as a check valve to allow flow in one direction.

Seal discs 46 and 50, along with the associated pressure line 52, gaslift valve 54, stinger tube 64 and standing valve 122, can be madeintegrally as one element so that they may be retrieved from productiontubing 26 in a manner very similar to a retrievable tubing stop commonlyused in the petroleum industry. By making the seal discs 46 and 50 inthe form of retrievable tubing stop, direct access may be obtained tothe accumulator 30 from the well head. Seal discs 46 and 50 are used forillustration purposes.

From space 48 a bypass tubing 66 extends upward and reconnects withproduction tubing 26. The purpose of the bypass tubing 66 is to extendaround free floating piston or swab 68 which is contained in theproduction tubing immediately above seal disc 46 with a heavy spring 70located therebetween. The free floating piston 68 may be of a typemanufactured by McMurry Oil Tools Inc. of Houston, Tex., having a tradename of McMurry Plunger. Other types of free floating pistons or swabscould be used in place of free floating piston 68 as long as a good sealis maintained between the free floating piston 68 and the internal wallsof production tubing 26.

At the surface of the hydrocarbon producing well is located the controlportion 72 of the artificial lift apparatus previously described aslocated in the well 10. The production tubing 26 has the typicalextended portion 74 to receive the free floating piston 68 whilesimultaneously routing the oil through horizontal tubing 76 to the oiltank. In the horizontal tubing 76 is located a check valve 78 that willpresent oil from flowing back into the well through production tubing 26once it has been received in horizontal tubing 76.

The vent/compressor line 28 is connected through a three-way solenoidoperated valve 80 to either compressed air or atmosphere. Asschematically shown in the present invention, the three-way solenoidoperated valve has a coil 82 and core 84 that moves with respect theretoaccording to the magnetic flux generated by the coil 82. To the core 84is connected a lever arm 86 which is pivotally connected to housing 88by pivot pin 90. On the opposite end of lever arm 86 is connectedpressure valve 92 and vent valve 94. Pressure valve 92 operates againstseat 96 while vent valve operates against seat 98. As shown in thedrawing, a three-way solenoid operated valve is energized, therebyforcing pressure valve 92 against seat 96 to stop the flow of compressedair through compressed air tubing 100. The compressed air may bereceived from any conventional means such as a compressor and associatedstorage tank that may be used for the entire oil producing field or forthe individual hydrocarbon producing well 10. The other side of thethree-way solenoid operated value (which is shown as being in fluidcommunication with the vent/compressor line 28) is connected to ventline 102. Vent line 102 is connected through pressure regulator 104 and(if necessary) choke 106 to atmosphere.

Pressure regulator 104, which may be the typical Big Joe Regulator"commonly used in the petroleum industry is installed in the reverse ofits normal operation. Therefore, if a pressure at point A in vent line102 exceeds a predetermined amount (25 pounds being typical) theregulator 104 will close, thereby preventing flow therethrough; however,any amount of pressure at point B in vent line 102 would not effect theoperation of the pressure regulator 104 unless the pressure is reflectedat point A. While the three-way solenoid operated valve 80 is in theposition shown in FIG. 1 so that the accumulator 30 is being vented, thepressure regulator 104 will remain open because the pressure at point Anever exceeds the operation point of the pressure regulator 104.

interconnecting tubing 108 connects vent line 102 with horizontal tubing76 that transports the oil to the oil tank. In the interconnectingtubing 108 is a check valve 110 that allows flow from interconnectingtubing 108 into horizontal tubing 76 but not vice versa. Therefore, if agreater pressure is reflected in interconnecting tubing 108 and than inhorizontal tubing 76, check valve 110 will open allowing flowtherethrough. An additional check value 112 in horizontal tubing 76 maybe necessary between interconnecting tubing 108 and production tubing 26as will be subsequently described.

To operate the three-way solenoid operated valve 80, a clock 114 andtimer 116 are necessary. The clock 114 and timer 116 may be of a typicaltype so that energy to the three-way solenoid operated valve 80 isinterrupted by terminating the power source for a predetermined periodof time. Connected to the compressed air tubing 100 and vent line 102are pressure switches 118 and 120, respectively. Pressure switch 118 isdesigned to close when compressed air of a predetermined value isavailable in compressed air tubing 100. Pressure switch 120 is anormally open type of pressure switch so that upon losing pressure thepressure switch will close, thereby forming a closed series circuit withtimer 116 to start the time period. As long as the vent- /compressorline 28 is venting from the accumulator 30, a slight pressure will befelt by pressure switch 120 because of the choke 106 in the vent line102. Pressure switch 120 is a standard off-the-shelf item that can sensean extremely low pressure difference created by the normal ventingthrough choke 106. Once enough oil has collected in the accumulator 30to reach the ball float chamber 38, the ball valve 40 will raise withthe oil level to interrupt the vent through vent/compressor line 28.Since no venting is now taking place, the pressure inside of vent line102 will drop to zero and pressure switch 120 will close, therebystarting the operation of the timer 116. Timer 116 will then interruptthe power that is being supplied through clock 114 to the three-waysolenoid valve 80 causing the pressure against pressure valve 92 toforce lever arm 86 downward which in turn connects the compressed air tothe vent/compressor line 28, and terminate the connection between thevent/compressor line 28 and atmosphere.

M ETHOD OF OPERATlON Once the artificial lift apparatus has beeninserted in the hydrocarbon producing well 10, oil begins to collect inthe accumulator 30 by entering through opening 34 and check valve 32.Once the oil in the accumulator 30 has raised to such a level that ballvalue 40 seals off the vent/compressor line 28, no more air can bevented from the accumulator 30. At the surface pressure switch 120 willsense a very small drop in pressure that will occur when the ventcompressor line 28 has been shut off. The amount of change in pressurereflected in vent line 102 and, consequently, at pressure switch 120 isvery small. As the remaining pressure in vent line 102 vents toatmosphere through choke 106 to approach zero pressure, the pressureswitch 120 will close to activate the timer 116. Since pressure switch120 is connected in series with pressure switch 118, compressed air mustbe connected to compressed air tubing 100 before the timer 116 isactivated. Pressure switch 118 is necessary where using a system ofwells operated by a single tank and compressor to insure there issufficient pressure before triggering the timer 116.

When timer 116 is activated, the power source received through clock 114and timer 116 to three-way solenoid operated valve 80 is terminated,thereby allowing the core 84 to move between the coil 82. Movement ofthe core 84 moves the lever arm 86 down and unseats pressure valve 92and seats vent valve 94. During the unseating of pressure valve 92 andthe seating of vent valve 94 a small pressure may be felt at point A andvent lines 102 causing the pressure regulator 104 to momentarily closeor chatter.

The compressed air is now fed through compressed air tubing 100,three-way solenoid operated valve 80, vent/compressor line 28 intoaccumulator 30. Check valve 32 prevents the pressurized air from forcingany of the oil back into th earth formation 14 or the hydrocarbonproducing zone 16. As pressure builds up in the top of the accumulator30, the oil will be forced downward and up through stinger tube 64,space 48, bypass tubing 66 into production tubing 26. As the pressurecontinues to increase in accumulator 30, more of the oil will move upthrough stinger tube 64. Once a predetermined pressure level has beenreached, the gas lift valve 54 will open, thereby introducingpressurized air immediately above seal disc 46 and below free floatingpiston 68. The point at which the gas lift valve 54 opens should be justbefore all of the oil in accumulator 30 has moved up through stingertube 64. Otherwise, the pressurized air entering accumulator 30 throughthe vent/compressor line would start to bubble through the stinger tube64, thereby creating an emulsion in the oil. Once the gas lift valve 54has been set to the approximate pressure this can be controlled bycontrolling the flow rate of the compressed air into the accumulator 30.A more rapid flow of compressed air into accumulator 30 would triggerthe gas lift valve 54 at an earlier point in time before as much of theoil has had a chance 8 to move up through stinger tube 64 intoproduction tubing 26.

As the pressurized air now moves into the zone between seal disc 46 andfree floating piston 68, the free floating piston will start to movetowards the surface of the hydrocarbon producing well 10. The freefloating piston 68 which has seals around the inside surface of thecasing 12 to prevent the oil from escaping back to the lower portion ofthe production tubing 26 begins moving upward. As the pressure isfurther increased all of the oil above free floating piston 68 and thefree floating piston 68 moves to the surface of the well 10. As the oilreaches the surface it is vented out through horizontal tubing 76 intothe oil tank. The extended portion 74 allows the free floating piston 68to be captured (if necessary) for entry into the well. Extra venting(not shown) may be necessary for the extended portion 74 as is common inconjunction with the use of free floating pistons or swabs.

The oil that is above the free floating piston 68 lifts check valves 112and 78 while flowing through the hor izontal tubing 76 into the oiltank. Once the present time of timer 116 has expired (said preset timeshould be sufficient to raise the piston 68 to the well head), thethree-way solenoid operated valve 80 will reenergize to close pressurevalve 92 and open vent valve 94. The pressure contained in accumulator30 and the vent- /compressor line 28 is now felt in vent line 102. Sincepoint A of vent line 102 now has a pressure that exceeds the pressurethat the regulator 104 is attempting to control, the pressure regulator104 will close. Therefore, the only path left for all of the airpressurized in accumulator 30 is through check valve 110 into horizontaltubing 76. This pressure will force check valve 112 to close and checkvalve 78 to remain open. The air pressure discharged from accumulator 30will now force the air in horizontal line 76 to move into the storagetank. If sufficient pressure was available in production tubing 26 andaccumulator 30, check valve 112 may not in fact be necessary. However,to insure that the pressurized air moves towards the oil tank instead ofback into the well 10, check valve 112 has been included. As thepressure in accumulator 30 and the vent/compressor line 28 continues todecrease, it will reach the set point for the pressure regulator 104.Once the set point has been reached at point A, the regulator 104 willagain open, thereby allowing the accumulator 30 to vent to atmosphere.Unless the free floating piston 68 is caught in the extended portion 74,it will be allowed to fall back down the production tubing 26 until ithits heavy spring 70. Heavy spring will absorb the impact of freefloating piston 68 to prevent damage to the apparatus containedtherebelow.

It should be realized that the three-way solenoid operated valve couldbe replaced with two indepen dent solenoid operated valves, with anormally closed valve being in compressed air tubing and 21 normallyopen valve being in vent line 102. Then the timer 116 wouldsimultaneously energize both valves upon receiving the signal frompressure switches 118 and 120.

Also, the three-way solenoid operated valve 80 has been described asbeing continuously energized when in fact it may be reverse type whereinthe lever arm 86 is biased upward and additional force of currentflowing through the coil 82 is necessary to overcome the bias againstthe lever arm 86.

There are various modifications of the artificial lift apparatusdescribed in the present invention such as the seal casing head, orpackers above and/or below the production zone. The accumulator 30 maybe of varying lengths with a typical length being possibly 100 feet. Howthe artificial lift apparatus is used with depend upon thecharacteristics of the individual well. Because of the extremesimplicity of the apparatus located at the bottom of the well, the lifeexpectancy of that portion of the apparatus located in the well isextremely long. Therefore, it now becomes economically feasible tocontinue to operate the hydrocarbon producing well much longer thanpreviously possible. Another reason that the productive life of the wellis now extended is because the pressure being fed into the well isapplied to a much smaller diameter area than the casing 12 as was thecase in the previous method of gas lift using a swab or free floatingpiston. Because the area of the casing 12 is much greater than the areaof the ventlcompressor line 28 and production tubing 26 it willwithstand much less pressure than is possible with the presentartificial lift apparatus. Assuming that surface power is lost on thecontrol portion 72 or it is shut off due to production requirements forthe field, oil may accumulate in the production tubing 26 to form an oilcolumn of a substantial height. Because of the smaller area of theproduction tubing 26 and the vent/compressor line 28, and due to specialconstruction of the accumulator 30, a rather substantial pressure can bebuilt up below free floating piston 68 to raise a rather substantialcolumn of oil in the production tubing 26 to the well head. Dependingupon the characteristics of the individual well, a number of differentmethods may be used to bring a well back into production.

The first and most obvious method is to use a portable compressor toincrease the pressure in the well to such an extent it will raise theentire column of oil to the well head. During normal production a muchsmaller and less expensive compressor may be used.

The second method would be to use a swab and line to swab out the wellby lowering the swab part of the distance into the accumulated oil andpulling the swab and oil to the well head by the line. This would berepeated until the column of oil is reduced and normal production may beresumed.

A third and more costly method would be to raise the accumulator in thecolumn of oil, and gradually lower the accumulator as the column of oilis decreased until normal production resumes.

If the alternative embodiment (subsequently described) is utilized, themethods immediately above of resuming normal production do not apply.

The particular stage in the productive life of a hydrocarbon producingwell wherein the present artificial lift apparatus becomes economicallyfeasible will vary. However, it could be used in the second stage inplace of gas lift especially when a ready source of gas is notavailable. The present apparatus which does not bubble the air throughthe oil does not create an emulsion which is harmful to the end product.

In the present artificial lift apparatus, by venting the accumulator tothe atmosphere, the hydrocarbon producing well may be economicallyfeasible to operate until the bottom hole pressure has reached zero. Inwells that have a sump bore below the pay zone, it may even beeconomically feasible to use the present artific ial lift apparatus inwells where the bottom hole pressure has decreased below zero. This typeof production will depend upon latent water drive, changes in the earth,underground formations, gravity, contributions from other zones notcompletely depleted, etc. By using the present artificial liftapparatus, hydrocarbon producing wells can be continually produced on aneconomical basis almost exponentially. In the petroleum industry, it isnot economically feasible to continue to operate the well beyond someminimum product per day depending on the individual well characteristic.Using the present type of artificial lift apparatus the well can beoperated long after other devices are no longer practical. Mosthydrocarbon producing wells are abandoned when they still haveapproximately forty or fifty percent of their theoretical productivecapacity remaining. The present artificial lift apparatus is designedprimarily for getting that extra forty or fifty percent from the wellplus decreasing the cost for artificial lift at earlier stages in theproduction life of the well.

ALTERNATIVE EMBODIMENT Referring now to FIG. 2 of the drawings, there isshown an alternative embodiment of the present invention. In thealternative embodiment, which is much simpler than the preferredembodiment, the piston 68 and spring 70 have been eliminated. Gas liftvalve 54, pressure line 52 and bypass tubing 66 are no longer necessaryso they have not been shown in FIG. 2. To change from the preferredembodiment to the alternative embodiment, the piston 68 should betrapped in extended portion 74. Thereafter, a line can be run into thewell and hooked on hook 124 to retrieve the appartus connected to discs46 and 50. By sealing gas lift valve 54 shut the same apparatus may belowered back into the well 10. Because discs 46 and 50 now function as asingle disc, they are incorporated in disc 51 of FIG. 2.

It should be realized that FIG. 2 shows only the essential components inthe well 10 rather than how it would have looked if the preferredembodiment of FIG. I had been changed to the alternative embodiment ofFIG. 2. Since the control portion above the well 10 is essentially thesame, it has not been shown again in FIG. 2.

In the alternative embodiment of FIG. 2, the accumulator 30 is vented toatmosphere through ball float valve 38. Same as previously discussed,when the ball float valve 38 blocks vent/compressor line 28 indicatingthe accumulator 30 is full of oil, the control portion 72 (see FIG. l-a)starts pressuring the accumulator 30 through vent/compressor line 28.Essentially, all the oil in accumulator is forced through the standingvalve 122 and stinger tube 64 into the production tubing 26. Now thecycle of the timer 116 is decreased so that the movement of the oil intothe production tubing 26 is the function accomplished. Afterwards, theaccumulator 30 is again vented to atmosphere to allow further collectionof oil in the accumulator 30. The cycle is repeated when the accumulator30 is full. This cycle is repeated again and again until the column ofoil in the production tubing 26 reaches the well head. Standing valve122 prevents the reverse flow of oil back into the accumulator. Furthercycles will now cause oil to flow in horizontal tubing 76 on each cycle.

It may be necessary to increase the time of each cycle while bringing awell into production because of the increased pressure necessary toforce the increasingly long oil column up the production tubing. Oncethe well starts flowing, the time cycle may be fixed. Otherwise, for afixed pressure, either the pressure will not be enough to bring the wellinto production, or an emulsion between the air and oil will be createdduring the initial cycles.

The stinger tube 64 could be a simple extension of the production tubing26 into the accumulator 30 without the necessity of seal disc 51. Theonly limitation on the alternative embodiment is the amount of pressurethat can be exerted on vent/compressor line 28, accumulator 30, andproduction tubing 26. Because of the decreased diameter when compared tocasing 12, a tremendously increased pressure can be exerted that couldnot be exerted on casing 12 of previous artificial lift system. Atypical diameter of the production tubing 26 could be 2 inches, thatdiameter combating flow resistance due to friction for smallerdiameters.

ln utilizing the present invention, a packer is not necessary. However,if circumstances of the well so dictate, such as a water zone above theoil zone or casing that has been blown off, a packer may be used. Byusing a packer, many wells that have been blown and plugged may bebrought back into production using the present invention on an economicbasis.

The individual characteristics of the well will dictate which of theembodiments of the present invention should be utilized. Because thealternative embodiment raised the entire column of oil to the well head,a much larger pressure is necessary than required for the preferredembodiment utilizing a piston. Therefore, if the well is too deep (alsoconsidering the other characteristics), the piston type of the preferredembodiment may be more practical because of the small compressornecessary for operating the well or system of wells. This determinationshould be made before initial installation, though the presentembodiments may be changed later with a minimum of effort.

What is claimed is:

1. An artificial lift apparatus for a liquid producing well having awell head and a well casing therein, said apparatus comprising:

production tubing extending from the well head into the casing to alevel below which the liquid will fill through perforations in thecasing; accumulator means surrounding the bottom of the productiontubing for collecting liquid in the well;

gas tubing means extending from the well head into the accumulator meansfor communication therewith from the well head;

first check valve means for only allowing flow of liquid into saidaccumulator means;

standing valve means at essentially the bottom of said production tubingto allow flow of said fluid only into said production tubing, saidbottom of said production tubing being near the bottom of saidaccumulator means;

means for receiving and handling said liquid at said well head; andcontrol means for alternatively venting and pressurizing saidaccumulator means via said gas tubing means, liquid being allowed tocollect in said accumulator means via said check valve means duringventing, thereafter in response to said pressurizing, said liquid ismoved through standing valve means into said production tubing andraising to the well head; said control means includes a normally openvalve connecting said gas tubing means to atmosphere, and a normallyclosed valve connecting said gas tubing means to a source of pressurizedgas, said normally open valve and said normally closed valve bothswitching in response to a control signal;

said control signal is generated by a first pressure switch in a ventline from said normally open valve to atmosphere, the lower end of saidgas tubing means having a float valve for closing upon the filling ofsaid accumulator means with liquid, said control signal being generatedupon closing said float valve and subsequent loss of pressure on saidfirst pressure switch.

2. The artificial lift apparatus as given in claim wherein said normallyopen valve and said normally closed valve are parts of a three-way meansoperated by said control signal, said control signal being maintainedfor a given time period by a timer, said time period being sufficient tomove liquid from said accumulator into said production tubing.

3. The artificial lift apparatus as given in claim I further includes apressure regulator between said normally open valve and atmosphere formaintaining pressure in said gas tubing means, alternative conduit andsecond check valve means connecting said normally open valve to saidmeans for receiving and handling said liquid at said well head, aftertermination of said control signal said pressurization of saidaccumulator means is discharged through second check valve means to movesaid liquid further along the receiving and handling means, third checkvalve means preventing said liquid from flowing back into said well.

4. The artificial lift apparatus as given in claim 1 wherein the portionof said production tubing extending into said accumulator is aretrievable sringer tubing means with said standing valve locatedtherein.

1. An artificial lift apparatus for a liquid producing well having awell head and a well casing therein, said apparatus comprising:production tubing extending from the well head into the casing to alevel below which the liquid will fill through perforations in thecasing; accumulator means surrounding the bottom of the productiontubing for collecting liquid in the well; gas tubing means extendingfrom the well head into the accumulator means for communicationtherewith from the well head; first check valve means for only allowingflow of liquid into said accumulator means; standing valve means atessentially the bottom of said production tubing to allow flow of saidfluid only into said production tubing, said bottom of said productiontubing being near the bottom of said accumulator means; means forreceiving and handling said liquid at said well head; and control meansfor alternatively venting and pressurizing said accumulator means viasaid gas tubing means, liquid being allowed to collect in saidaccumulator means via said check valve means during venting, thereafterin response to said pressurizing, said liquid is moved through standingvalve means into said production tubing and raising to the well head;said control means includes a normally open valve connecting said gastubing means to atmosphere, and a normally closed valve connecting saidgas tubing means to a source of pressurized gas, said normally openvalve and said normally closed valve both switching in response to acontrol signal; said control signal is generated by a first pressureswitch in a vent line from said normally open valve to atmosphere, thelower end of said gas tubing means having a float valve for closing uponthe filling of said accumulator means with liquid, said control signalbeing generated upon closing said float valve and subsequent loss ofpressure on said first pressure switch.
 2. The artificial lift apparatusas given in claim wherein said normally open valve and said normallyclOsed valve are parts of a three-way means operated by said controlsignal, said control signal being maintained for a given time period bya timer, said time period being sufficient to move liquid from saidaccumulator into said production tubing.
 3. The artificial liftapparatus as given in claim 1 further includes a pressure regulatorbetween said normally open valve and atmosphere for maintaining pressurein said gas tubing means, alternative conduit and second check valvemeans connecting said normally open valve to said means for receivingand handling said liquid at said well head, after termination of saidcontrol signal said pressurization of said accumulator means isdischarged through second check valve means to move said liquid furtheralong the receiving and handling means, third check valve meanspreventing said liquid from flowing back into said well.
 4. Theartificial lift apparatus as given in claim 1 wherein the portion ofsaid production tubing extending into said accumulator is a retrievablesringer tubing means with said standing valve located therein.